REST风格

（资源）表现层状态转化，是一种目前最流行的互联网软件架构，主要是用来要求URL地址的！
系统希望以非常简洁的URL地址来发请求；
怎样表示对一个资源的增删改查用请求方式来区分

例如:（以前的方式）

getBook?id=1
updateBook?id=1bookName=aaa
deleteBook?id=1
addBook?bookName=1

Rest推荐：

url地址这么起名：/资源名/资源标识符

/book/1     :GET----查询1号图书
/book/1     :PUT----更新1号图书
/book/1     :DELETE----删除1号图书
/book        :POST----添加1号图书

系统的URL地址就这么来设计，简洁的URL提交请求，以请求方式区分对资源的操作。
问题：从页面上只能发起两种请求，GET、POST
其他的请求方式没法使用：

使用Rest来构造一个CRUD系统

从页面发起PUT，DELETE形式的请求?Springr提供了Rest风格的支持

1.springMVC有一个Filter，可以把请求转化了规定形式的

<filter>  
    <filter-name>HiddenHttpMethodFilter</filter-name>  
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
</filter>
<filter-mapping>  
    <filter-name>HiddenHttpMethodFilter</filter-name>  
    <url-pattern>/*</url-pattern>
</filter-mapping>

2.如何发其他形式请求？

1.创建一个post类型的请求

2.表单项中携带一个_method的参数

3.这个_method的值就是DELETE、PUT

一个CRUD的小Demo

<a href="book/1">查询图书</a>

<form action="book" method="post">   
    <input type="submit" value="添加1号图书"/>
</form><br/>

<form action="book/1" method="post">    
    <input name="_method" value="delete">   
    <input type="submit" value="删除图书"/>
</form><br/>

<form action="book/1" method="post">  
    <input name="_method" value="put">  
    <input type="submit" value="更新图书"/>
</form><br/>

success.jsp(注意如果是其他的请求时，成功页面必须加isErrorPage="true")

<%@ page contentType="text/html;charset=UTF-8" language="java" 
isErrorPage="true" %>
<html>
<head>    
<title>Title</title>
</head><body>    
<h1>你成功了，666666</h1>
</body></html>

BookController.class

@Controller
public class BookController {

    @RequestMapping(value = "/book/{bid}",method = RequestMethod.GET)
    public String addBook(@PathVariable("bid") Integer id){
        System.out.println("查询到了"+id+"号图书");
        return "success";
    }

    @RequestMapping(value = "/book/{bid}",method = RequestMethod.DELETE)
    public String deleteBook(@PathVariable("bid") Integer id){
        System.out.println("删除了"+id+"号图书");
        return "success";
    }

    @RequestMapping(value = "/book/{bid}",method = RequestMethod.PUT)
    public String updateBook(@PathVariable("bid") Integer id){
        System.out.println("更新了"+id+"号图书");
        return "success";
    }


    @RequestMapping(value = "/book",method = RequestMethod.POST)
    public String getBook(){
        System.out.println("添加了新的图书");
        return "success";
    }
}

web.xml

<display-name>Archetype Created Web Application</display-name>

 <filter>
   <filter-name>characterEncodingFilter</filter-name>
   <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
   <init-param>
     <param-name>encoding</param-name>
     <param-value>UTF-8</param-value>
   </init-param>
   <init-param>
     <param-name>forceEncoding</param-name>
     <param-value>true</param-value>
   </init-param>
 </filter>
 <filter-mapping>
   <filter-name>characterEncodingFilter</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>


 <servlet>
   <servlet-name>dispatcherServlet</servlet-name>
   <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
   <init-param>
     <param-name>contextConfigLocation</param-name>
     <param-value>classpath:springmvc.xml</param-value>
   </init-param>
   <load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
   <servlet-name>dispatcherServlet</servlet-name>
   <url-pattern>/</url-pattern>
 </servlet-mapping>

 <filter>
   <filter-name>HiddenHttpMethodFilter</filter-name>
   <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
 </filter>
 <filter-mapping>
   <filter-name>HiddenHttpMethodFilter</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>

运行结果
我们来看一下请求过滤方法HiddenHttpMethodFilter的源码

public class HiddenHttpMethodFilter extends OncePerRequestFilter {

    /** Default method parameter: {@code _method} */
    //接收带来的_method中的值 
    public static final String DEFAULT_METHOD_PARAM = "_method";

    private String methodParam = DEFAULT_METHOD_PARAM;


    /**
     * Set the parameter name to look for HTTP methods.
     * @see #DEFAULT_METHOD_PARAM
     */
    //初始化方值 
    public void setMethodParam(String methodParam) {
        Assert.hasText(methodParam, "'methodParam' must not be empty");
        this.methodParam = methodParam;
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        HttpServletRequest requestToUse = request;
            //如果是post方法并且没有异常
        if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
        //拿到这个请求中的参数
            String paramValue = request.getParameter(this.methodParam);
            //判断长度是否为空
            if (StringUtils.hasLength(paramValue)) {
//然后调用HttpMethodRequestWrapper将参数转换为大写
//然后new了一个新的HttpMethodRequestWrapper，最后用新传进来的method重写了原来的getMethod
                requestToUse = new HttpMethodRequestWrapper(request, paramValue);
            }
        }

        filterChain.doFilter(requestToUse, response);
    }
private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {

        private final String method;

        public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
            super(request);
            this.method = method.toUpperCase(Locale.ENGLISH);
        }

        @Override
        public String getMethod() {
            return this.method;
        }
    }

REST